This invention relates to a magnetic tape cartridge formed by ultrasonic welding.
In FIG. 1, reference numeral 1 designates the magnetic tape cartridge. The magnetic tape cartridge 1 is constructed as follows: A magnetic tape 20 is wound on a reel 3 which is formed by combining upper and lower reels 4 and 5 together by ultrasonic welding. The reel 3 is rotatably accommodated in a cartridge casing which is formed by combining upper and lower cartridges 2a and 2b together with screws 19.
The upper reel 4 is made of polycarbonate resin containing glass fibers. The upper reel 4 has an upper flange 4a, and a recess at the center which has a boss section 4b extended towards the center. The upper flange 4a has a gear 4y on its outer cylindrical surface.
The aforementioned recess has a cylindrical rib, in which a ring-shaped bearing 6 is press-fitted. And a spring plug 7 is fixedly press-fitted in the central hole formed in the bearing. A reel spring 8 is mounted on the spring plug 7, to push downwardly the aforementioned reel 3 and hold the reel 3 rotatably.
The lower reel 5 is made of polycarbonate resin, and has a lower flange 5a which has a hole at the center around which an ultrasonic welding rib 5b is formed. The lower reel 5 is combined with the shoulder of the aforementioned boss section 4b. 
When the cartridge is not in use, the reel 3 is locked by reel brakes 50 and 51 so that it may not be turned unintentionally, the reel brakes 50, 51 which are suitably urged by braking torsion springs 12. When the magnetic tape cartridge 1 is not in use, the magnetic tape 20 has been completely wound on the reel 3, and the leader tape. 21 connected to the end of the magnetic tape is locked to the end of a hook 18 which is provided near the side wall of the cartridge.
The opening, through which the magnetic tape 20 is pulled out is designed as follows: That is, a lid 30, which is swingable in a cartridge plane, is provided while being suitably urged by a torsion spring 15. When the cartridge is not in use, the lid 30 is locked by a locking member 40 (which is suitably urged by a compression spring 16) so that it may not be swung. On the side which is opposite to the side where the lid 13 is provided, the cartridge has a write protect 17.
The aforementioned leader tape 21 is engaged with an engaging means adapted to lead the magnetic tape 20 in the tape path of the recording and reproducing device. The leader tape 21 is fastened to the magnetic tape 20, for instance, by splicing.
In the above-described magnetic tape cartridge 1, the upper and lower reels 4 and 5 are combined together by ultrasonic welding as follows. As was described before, the annular rib 5b, which is formed along the annular edge of the circular opening formed at the center of the lower flange 5a, is engaged with the shoulder of the lower portion of the boss section 4b. Under this condition, while a predetermined pressure is applied to the upper and lower reels 4, 5, those reels 3 are subjected to ultrasonic excitation, so that the rib 5b is molten to combine the upper and lower reels 4 and 5 together.
In this welding operation, the upper reel 4 is set below the lower reel 5. More specifically, the upper reel 4 is fixedly set, and the lower reel 5 is placed on the upper reel 4 from above. Under this condition, the upper reel 4 is subjected to ultrasonic pressure excitation. As the rib 5b is molten, the surface of the lower reel 5 is brought into contact with the shoulder of the upper reel 4. From this fact, it is determined that the welding operation has been accomplished.
FIG. 2 shows the conventional ultrasonic welding portions of the aforementioned reel 3. The boss section 4b of the upper reel 4 comprises a shoulder 4c, and a protrusion 4d which is extended from the shoulder 4c and is smaller in diameter than the shoulder 4c. Along the outer annular edge of the shoulder 4c, a stopper ring 4e is integrally provided which is slightly higher in level. That is, the upper reel 4 is in the form of a shallow-bottomed container as a whole. In addition, between the stopper ring 4e and the protrusion 4d, turn-preventing stoppers 4f are provided in such a manner that they are diametrically opposite to each other, and are flush with each other.
On the other hand, the rib 5b of the lower reel 5 has cuts 5d at angular intervals of 90xc2x0. When, with the central hole of the lower reel 5 engaged with the protrusion 4d of the upper reel 4, the lower reel 5 is turned, the cuts 5d are engaged with the turn-preventing stoppers 4f. When, under this condition, the reel 3 is subjected to pressure excitation, the rib 5b is molten. The molten portion of the rib 5b, being absorbed in the shallow-bottomed annular groove, is spread uniformly. As a result, the surface of the lower flange 5a is brought into contact with the upper surface of the stopper ring 4e. Thus, the welding operation has been accomplished.
In the above-described conventional magnetic tape cartridge, the lower flange 5a and the stopper ring 4e are almost in line contact with each other; that is, they are considerably small in contact area. Hence, it is difficult to weld the upper and lower reels 4, 5 together in such a manner that they are high in parallelism. This fact results in a so-called surface play.
In the case where the tape 20 is wound on the reel 3, the tape winding operation is carried out with the upper flange 4a and the boss section 4b of the upper reel 4 as a reference. In this case, since the upper flange 4a and the boss section 4b are formed as one unit by injection molding, the tape 20 can be wound on the reel 3 with high accuracy. However, in the case where the tape winding operation is carried out based on the lower reel 5 and the boss section 4b which suffer from the surface play, it is difficult to achieve the tape winding operation with high accuracy.
If, with the reel 3, the welding area is increased in the direction of the diameter, the width of the stopper ring 4e should be increased. However, in this case, the molten portion flows out of the shallow-bottomed groove; that is, the resultant product is unacceptable. In addition, the welding area is not large enough; that is, the upper and lower reels 4, 5 are not satisfactorily welded together.
In the case of the conventional reels 3 shown in FIG. 2, the lower reel 5 is prevented from turning as follows: That is, in order to prevent the lower reel 5 from turning, after the lower reel 5 is set on the upper reel 4, the lower reel 5 must be turned at most 90xc2x0. Accordingly, it is impossible to subject the upper and lower reels 4, 5 to ultrasonic work immediately after the lower reel 5 is set on the upper reel 4. Furthermore, a metal mold for forming the turn-preventing stoppers 4f and the cuts 5d is intricate in configuration. Therefore, there is a strong demand for the provision of turn-preventing means which replaces the turn-preventing stoppers 4f and the cuts 5d. 
Furthermore, in the conventional magnetic tape cartridge, as shown in FIG. 3(a) the rib 5a is molten starting from its end by pressure excitation, and the molten resin spreads gradually in the shallow-bottomed groove according to the pressure.
However, in practice, as indicated by a group of dots in FIG. 3(b), owing to the pressure which is applied simultaneously when the melting operation starts a part of the molten resin sometimes flows over the stopper ring 4e to the outer periphery of the boss section 4b. The molten resin thus caused to over-flow is solidified as cooled, thus sticking onto the outer periphery. Hence, when the tape 20 is wound on the reel 3, the winding center is shifted from the true center; that is, the resultant product is unacceptable.
Accordingly, an object of the invention is to provide a magnetic tape cartridge in which the above-described difficulties accompanying a conventional magnetic tape cartridge have been eliminated.
Accordingly, a first object of the invention is to provide a magnetic tape cartridge having a reel which is high in weldability, and is so shaped that it is increased in the area of a stopper surface during welding, whereby the upper and lower reels are sufficiently high in parallelism.
The first object of the invention has been achieved by the provision of a magnetic tape cartridge having a reel which comprises an upper reel and a lower reel which are plastic moldings, the lower reel being welded to the upper reel by ultrasonic welding;
in which, according to the invention,
in the shoulder of a boss section of the upper reel, a plurality of recesses are formed in such a manner that the recesses are radially outwardly extended from the center of rotation of the upper reel, and
on the surface of the lower reel which are confronted with the recesses, a plurality of welding ribs are formed so as to be engaged with the bottoms of the recesses.
Furthermore, the first object has been achieved by the provision of a magnetic tape cartridge having a reel which comprises an upper reel and a lower reel which are plastic molding, the lower reel being welded to the upper reel by ultrasonic welding;
in which, according to the invention,
on a shoulder surrounding the recesses of the upper reel, welding stopper surfaces are provided in such a manner that the welding stopper surfaces are scattered circumferentially over the whole width of the shoulder.
According to the invention, during ultrasonic welding, the molten ribs form flows of resin only in the recesses, so that the welding operation is achieved with an amount of welding resin corresponding to the number and area of recesses.
Furthermore, with the whole surface of the shoulder surrounding the recesses of the upper reel as the stopper surface, the welding surface spreads radially outwardly, so that the surface contact of the upper and lower reels which have been welded together are high in parallelism.
In the invention, the welding ribs may be extended radially outwardly from the peripheral edge of the central hole of the lower reel, or they may be curved spirally from the peripheral edge of the central hole, or they may be protruded in such a manner that they are coaxial with the peripheral edge of the central hole.
A second object of the invention is to provide a magnetic tape cartridge in which the above-described difficulties accompanying a conventional magnetic tape cartridge have been eliminated, and in which, immediately after the lower reel is set on the upper reel, those reels can be subjected to ultrasonic welding as they are (without turning the lower reel), and a reel metal mold is simple in construction.
The second object has been achieved by the provision of a magnetic tape cartridge having a reel which comprises an upper reel and a lower reel which are thermoplastic resin moldings, the lower reel being welded to the upper reel by ultrasonic welding with a welding rib protruded from the lower reel abutted against the shoulder of a boss section protruded from the upper reel,
in which, according to the invention,
the surface of the shoulder of the upper reel is roughened.
According to the invention, the lower reel is set on the upper reel, and under this condition, those reels are pressurized. As a result, the welding rib is pushed against the roughened surface to provide a frictional force which prevents the reels from turning circumferentially. This makes it possible to subject the reels to ultrasonic welding. The surface roughing metal molding is not intricate in structure when compared with the conventional one.
A third object of the invention is to provide a magnetic tape cartridge in which the above-described difficulties accompanying a conventional magnetic tape cartridge have been eliminated, and which has a reel in which, when the reel is manufactured, the molten resin is prevented from flowing over the outer periphery of the boss section to prevent the formation of an unsatisfactory product thereby to improve the product yield.
The third object of the invention has been achieved by the provision of a magnetic tape cartridge having a reel which comprises an upper reel and a lower reel which are thermoplastic resin moldings, the lower reel being welded to the upper reel by ultrasonic welding with a welding rib protruded from the lower reel abutted against the shoulder of a boss section protruded from the upper reel,
in which, according to the invention,
the surface of the shoulder of the upper reel is roughened.
In the invention, even if, during ultrasonic welding, the molten resin tends to flow over the outer periphery in response to a pressurizing force applied thereto, the over-flow of the molten resin is stopped because the gap provided the walls are narrowed.
The nature, utility and principle of the invention will be more clearly understood from the following detailed description and the appended claims when read in conjunction with the accompanying drawings.